Dental waxes are among the routine laboratory materials used in dentistry. For successful lab procedures it is necessary to amplify the material knowledge.
4. Definition
One of several esters of fatty acids with higher alcohols, usually
monohydric alcohol, dental waxes are combinations of various types of
waxes compounded to provide desired physical properties.
(G.P.T. 9th Edn. 2017)
5. History
One of the oldest natural substances used by man as diet source obtained
from insects.
Oldest was used is beeswax.
It was used for softening skin, binding together reeds used for flutes,
coating and preserving valuable objects, candle production, and making
sculptures
Greek & Roman Literature – Used for sealing ships, as binder matrix, for
protective coating of art objects, tablets etc.
(S.Mahalaxmi: Materials used in Dentistry)
6. 3000 BC- Beeswax used by Egyptians in
mummification process.
1700s- Mattheus Gottfried Purmann used
wax models for prosthetic work.
1935- First synthetic liquid paraffin was
produced by Fischer- Tropsch procedure.
(Phillips science of dental materials 12th ed.)
7. Classification
Type of wax Examples Sources
Plants wax Carnauba wax Carnauba palm
(leaves)
• Copernica cerifera
Candelilla wax Mexican shrubs
• Euphorbia cerifera
• Euphorbia
antisyphilitica
Japan wax Berries of
• Rhus species
• Toxicodendron
species
Insect wax Beeswax Honey bees
Shellac wax Lac insect
• Kerria lacca
Animal wax Lanolin Sebaceous glands of
sheep
Spermaceti Head cavities and
blubber of the sperm
whale
According to their source
8. Type of wax Examples Sources
Petroleum
waxes
Paraffin wax Petroleum
manufacturing
processMicrocrystalline
waxes
Mineral wax Ozokerite Lignite beds
Ceresin Ozokerite, a naturally
occurring mineral
wax
Montan wax Lignite and brown
coal
9. Based upon their uses classified into three types
Craig R. G. (1985 )Restorative dental materials 7th ed.
Pattern waxes Inlay wax
Resin wax
Casting wax
Baseplate wax
Impression wax Corrective wax
Biteplate wax
Soft impression wax
Disclosing wax
Processing wax Boxing wax
Beading wax
Sticky wax
Carding and blockout wax
White and utility waxes
10. Type I (Inlay casting wax)
Class 1 : Soft
Class 2 : Hard
Type II (Baseplate wax)
Class 1 : Soft
Class 2 : Hard
Class 3 : Extra hard
ADA/ISO Classification(ADA SP NO 12 /ISO 15854:2005)
11. Composition
Wax is a very complex mixture of many different types of compounds.
Defined as a substance that is solid at ambient temperature and when
subjected to moderate temperatures, becomes a low viscosity liquid.
Waxes used in dentistry may be composed of several ingredients,
including natural waxes, synthetics waxes, natural and synthetics resins,
and other additions such as oil, fats, gums, fatty acids, and coloring
agents of various types
Zhang: Rheological Characterization of Dental Waxes
12. Mineral waxes :
Made up of hydrocarbons ranging from 17 to
over 44 carbon atoms
CH3—(CH2)—CH3
15 to 42
13. Plant & Animal waxes :
contain considerable concentrations of esters
also contain acid, alcohols, and resins
Japan wax
Not true waxes but are chiefly fats
Improves tackiness and emulsifying ability of paraffin
15. Paraffin Waxes :
Composed mainly of a complex mixture of chiefly straight saturated
hydrocarbon chains possessing 26 to 30 carbon atoms of the methane
series.
Refining waxes and have less than 0.5% oil, which can lower the melting
temperature.
They crystallize in the form of plate, needles, or malcrystals but generally
are of plate type
16. During solidification and cooling, there is a volumetric contraction that
varies from 11% to 15%.
It likely to flake when it is trimmed, and it does not present a smooth,
glossy surface, which is desirable requisite for an inlay wax.
Other waxes and natural resins are added as modifying agents
17. Bees Waxes :
Primary insect wax used in dentistry, obtained
from honeycombs.
Complex mixture of esters consisting mainly of
mircyl palmitate plus saturated and unsaturated
hydrocarbons.
It is a brittle material at room temperature but
becomes plastic at body temperature
18. Carnauba waxes :
Composed of straight-chain esters, alcohols, acids, and
hydrocarbons.
They are characterized by quite high hardness,
toughness, brittleness, and high melting points from 65°C
to 9 0°C.
19. Cocoa butter
Contains glycerides of palmitic, stearic, oleic, lauric and lower
fatty acids.
Brittle at room temperature.
Primarily used to protect the soft tissues against dehydration
and also to protect the glass ionomer from moisture during
setting
20. Microcrystalline waxes :
Produced from a combination of heavy lube distillates and residual oils
in the petroleum industry or from crude oil tank bottoms.
Mixtures of solid, purified, mainly branched chain saturated
microcrystalline hydrocarbons monocyclic and polycyclic compounds .
They differ from paraffin waxes in that they have poorly defined,
extremely smaller crystalline structure, darker color, and generally
higher viscosity and melting range 65°C to 90°C.
21. Physical properties of dental waxes
I. General Physical Properties
Melting Range
Thermal expansion
Dimensional stability
Ductility
II. Mechanical Properties
Flow
Residual stress
22. Melting range
Waxes have melting ranges rather than melting point.
It varies depending upon their uses
Impossible to obtain precise values for the top and bottom of the
melting range because of the strong chemical similarities of
components.
23. Thermal Expansion
Waxes expand when subjected to a rise in temperature and contract
as the temperature is decreased.
Dental waxes and their components have the largest coefficient of
thermal expansion .
Reiber and Hupfauf, S. tested three bite registration waxes (Kerr No.8-
wax, Beauty Pink Hardwax and Aluwax) for their thermic dimensional
behaviour under several heating and cooling conditions.
24. They should not be heated more than necessary for achieving a
sufficiently plastic quality for use
It should be stored in ice water to be resistant enough to deformation
during the model mounting.
They Concluded..
25. Ductility
Increases as the temperature is increased
Greatly influenced by the distribution of the melting temperature.
Waxes with lower melting temperatures have a greater ductility at any
temperature than those with higher melting temperatures have.
26. Residual stress
Exists in the completed pattern, regardless of the method used to
prepare a wax pattern.
The warpage is due to the residual stresses which result from the
heating of wax specimens formed under compression or tension.
The longer the wax pattern is left before being invested, the greater the
distortion that must be result.
The effects are minimized by storing the shaped wax for the minimum
possible period (eg. the wax pattern for an inlay) and at reduced
temperature.
27. Flow
Flow of waxes is clearly important, not only as part of the deliberate
moulding process but also an undesirable aspect after the pattern.
A direct relationship was found between the flow of the wax and the
casting shrinkage
Flow is dependent on:
Temprature of the wax
Force applied
Length of time the force is applid.
28. Ito et al - investigated the relationship between flow
charcteristics, bending strength, and softening temperature of
paraffin and dental inlay waxes to casting shrinkage.
They found that the casting shrinkage decreased as the flow of
wax pattern increased.
Ito, M., Yamagishi, T. , Oshida, Y. et al. (1996)
Effect of selected physical properties of waxes on investments and casting shrinkage
J Prosthet Dent. 75, 211-216
29. Processing wax
Boxing & Beading wax
Uses
• Used to build up the vertical walls
around the impressions, in the order to
pour the stone and make a cast.
• The procedure is known as boxing.
Supplied as
• Boxing wax as sheets, beading wax as
strips.
30. Utility wax
Consists mainly of beeswax, petrolatum, and
other soft waxes in varying proportions.
Available in the form of sticks and sheets.
Used to adjust the contour of perforated tray
and for use with hydrocolloids.
31. Sticky wax
consists mainly of yellow beeswax, rosin,
and natural resins such as gum dammar
Properties:
It is brittle at room temperature and
assumes a thick liquid consistency when
heated.
It does not have more than 0.2% residue
burnout and not more than 0.5%
from 43°C to 28°C.
32. Uses
It holds broken pieces of a denture together and assembles
components of fixed partial dentures and wrought partial dentures
in preparation for soldering
33. Impression wax
Corrective Wax
It is formulated from hydrocarbon waxes such as paraffin,
ceresin, and beeswax and may contain metal particles.
Properties and uses
It has 100% flow at 37 C.
It is indicated only for edentulous impressions, since it
distorts on removal from the undercut areas.
It is used as a wax veneer over an original impression to
contact and register the detail of the soft tissue.
34. Bite registration wax
Formulated from beeswax or hydrocarbon
waxes such as paraffin or ceresin and may
contain alumina or copper particle.
Supplied as U-shaped rods or wafers
35. Steps in bite registration
1. The wax is softened in warm water. The soft wax is then
placed between the teeth and the patient is asked to bite.
2. It is then taken out and placed in chilled water.
3. The casts of the patient is placed in the indentations
formed by the teeth.
4. It is then mounted with plaster on the articulator.
36.
37. Pattern wax
Baseplate wax or Modeling wax
ADA SPECIFICATION NO. 24
Used in the construction of dentures and other
appliances made of acrylic and like materials.
38. Composition
composed mainly of paraffin, ceresin, beeswax, carnauba wax, and
coloring matter, which are mixed together, cast into blocks, and rolled
into sheets.
sheets are red or pink, 8.5-cm wide, 15-cm long, and 1.5-mm thick
39. Ideal requirements
1. It must be capable of holding porcelain or acrylic teeth in position both at
normal room temperature and at mouth temperature.
2. Softened sheets must cohere readily.
3. It should not be flaky or adhering to fingers.
4. It should not cause irritation of oral tissues.
5. It must be easy to trim with a sharp instrument at 23°C.
6. It must have a smooth surface after gentle flaming.
7. It must leave no residue on porcelain or plastic teeth during processing.
8. The coloring should not separate or impregnate plaster during processing.
40. Types
depending on the melting range
• Type 1: Soft wax used for building contour and veneers.
• Type 2: Medium wax used for fabrication of patterns in mouth. This
type of wax is preferred in temperate conditions.
• Type 3: Hard wax used for fabrication of pattern in the mouth.
41. Uses
1. Making occlusal rims and registering the vertical dimension
2. Holding artificial teeth to base plates
3. Extension of the impression tray
4. Patterns for orthodontic appliances
5. Spacer in custom tray for complete denture
6. Checking the occlusal clearance after crown preparation
42. INLAY WAX
ADA SPECIFICATION NO. 4; ISO 15854
Inlay wax is a specialized dental wax that can be applied onto the
prepared cavity or to the dies to form direct or indirect patterns
Can be classified into two groups.
type I inlay waxes(Medium wax): used in the mouth for direct
waxing processes for pattern production
type II inlay waxes(Soft wax): for making patterns on patients’ models
using the indirect wax technique
43. Ideal requirements of inlay wax
1. It must be able to closely adapt to the prepared portions of the tooth .
2. It should have low CTE.
3. It must have good cohesion, but should not adhere to the cavity walls.
4. It must permit detailed carving without flaking or chipping.
5. It must not leave any residue when the wax is eliminated from the mold.
44. 6. It should harden at oral temperature and remain plastic at
temperatures slightly above oral temperature without injury to pulp or
oral tissues.
7. At oral temperature, type I inlay wax must have essentially limited
flow
8. Its color should contrast with the colors of teeth and oral tissues to
facilitate carving.
45. 9. It must also be able to disintegrate, volatilize, and be eliminated
completely from an investment mold during the burnout or wax
elimination procedure.
10. If applied as a veneer in a sufficient thickness, its opacity must be
sufficient to mask colored die stones.
11. The flow should be more than 70% at 45°C and less than 1% at 37°C.
46. Composition of inlay wax
Composed of
Paraffin wax,
Gum dammar,
Carnauba or candellila
Ceresin.
Coloring agent
47. Role of individual component
Paraffin wax (40-60%)
Main ingredient
Used to establish the melting point
likely to flake when it is trimmed, and it does not produce a smooth,
glossy surface, which is a desirable requisite for an inlay wax.
Ceresin (10%)
Partially replaces paraffin
Increases toughness
Easy to carve
48. Gum dammar (1%)
It is a natural resin
Derivative from pine tree improves the smoothness in moulding
and makes it more resistant to cracking and flaking
It also increases toughness of the wax and enhances the luster of
the surface.
49. Carnauba wax (25%)
Decreases the flow at mouth temperature
It has an agreeable odor and gives glossiness to the wax surface
Candellila wax
Can be added to replace carnauba wax
melting is lower and is not as hard as carnauba wax
50. Synthetic waxes
Carnauba wax is often replaced partly by certain synthetic waxes
(Montan).
Their high melting point can imprpve general working qualities.
51. Properties of inlay wax
Thermal properties
Inlay waxes are softened with heat, forced into the prepared tooth
cavity in either the tooth or the die, and cooled.
The thermal conductivity of the waxes is low (e.g., kparaffin = 0.25
W/mK)
High coefficient of thermal expansion.
CTE for inlay wax is 350*10 per degree centigrade.
Philips science of dental maerials: 12th ed.
52. Expand as much as 0.7% with an increase
in temperature of 20 °C.
Contract as much as 0.35% when it is
cooled from 37 °C to 25 °C.
Philips science of dental maerials: 12th ed.
53. glass transition temperature
Abrupt change in the rate of expansion at
certain point of temperature occurs.
In the curve the change is at 35 degree.
It is known is glass transition temp.
Constituents of the wax probably change in
their crystalline form.
The wax is more plastic at higher
temperatures
Philips science of dental maerials: 12th ed.
54. Physical properties
Contact angle
It has low contact angle.
Wet the surface of the material to which it is being added
Flow
It should exhibit a marked plasticity or flow at a temperature slightly
above that of the mouth.
The flow is measured by subjecting cylindrical specimens to a
designated load at the stated temperature and measuring the
percentage of reduction in length
55. Requirements for Inlay Wax Flow (%)
Type of wax T = 30 °C
Maximum
T = 37 °C
Maximum
T = 40 °C
Minimum
T = 40 °C
Maximum
T = 45 °C
Minimum
T = 45 °C
Maximum
I - 1 - 20 70 90
II 1 - 50 - 70 90
ADA specification no. 4
56. Ductility
Have moderate ductility.
Wax distortion
The most serious problem one can
experience in forming and
the pattern from a tooth or die.
57. Causes of distortion
Occluded air in the pattern
Physical deformation (during molding, carving, or removal), release of
stresses “trapped” during previous cooling.
Excessive storage time.
Extreme temperature changes during storage.
If not held under uniform pressure during cooling.
58. Elastic memory
Waxes tend to return partially to their
original shape after manipulation.
To demonstrate this effect, a stick of
inlay wax can be softened over a
Bunsen burner, bent into a horseshoe
shape, and chilled in this position.
If it is then floated in room-
temperature water for a number of
hours, the horseshoe will open.
Philips science of dental maerials: 11th ed.
59. To Avoid distortion
Minimal carving and change in temperature.
Minimal storage of pattern, invest immediately.
Store it in a refrigerator if necessary
60. Manipulation of Inlay wax
Direct technique
Hold the stick of wax over the flame
and rotate it rapidly until it
becomes plastic.
The soften wax shaped
approximately to the prepared
cavity.
61. Insert the wax into the cavity and held under
finger pressure until it solidifies.
The wax should be allowed to cool gradually
to mouth tempreture.
Cold carving instrument should be used.
Withdraw the patern carefully in the long
axis of the tooth
The pattern shoud be touched as little as
possible with hands to avoid temperature.
62. Indirect technique
Pattern is prepared on the lubricant die.
i) Dipping method: The die can be dipped
repeatedly in the hot liquid wax
ii) Addition : The melted wax may be added
layers with a spatula or a waxing
63. ACCORDING TO MARZOUK
The 4 basic methods to produce wax replica of cast
restorations are:-
1) To create a wax mass, then carve it to the restoration
shape, using hot sharp instruments.
2) To incrementally built up the restoration, using wax
cones, triangles, drops, etc.
3) Fabricate wax pattern directly intra orally
4) Depends on Pre-operative anatomic core.
Marzuck’s modern operative dentistry
64. WAXING INSTRUMENTS
CARVING
WAX ADDING
BURNISHING
PKT instruments ( designed by Dr. Peter K. Thomas) are specifically used.
PKT No 1 & 2 – wax addition instruments
PKT No 3 - burnisher for refining occlusal anatomy
PKT No 4 & 5 – wax carvers
66. RPD Casting wax
They are available in the form of sheets.
An ideal casting wax copies accurately the surface against which
it is pressed.
It should not be brittle on cooling.
Uses
To make pattern of metallic framework of RPD.
67. Properties
They are tacky and ductile.
Maximum flow at 35°C is 10% and the minimum flow at 38°C is 60%.
It vaporizes at 500°C, leaving no residue
69. Effect on general health
Inhalation of paraffin wax vapours may cause respiratory irritation.
Molten wax causes burns and possible blindness in contact with eyes.
Molten wax causes burns on contact with skin
On swallowing the material is generally not toxic.
Material Safety Data Sheet in Accordance with 91/155/EEC & ANSI 400.1.2003
70. EXPOSURE CONTROLS / PERSONAL PROTECTION
Long term exposure limit (8hr ) – 2mg/m3
Short term exposure limit (10 min) – 6mg/m3
Respiratory protection: Adequate ventilation when heating wax
above 150C
Hand protection: Heavy duty butyl rubber gloves to be worn when
handling molten wax.
Eye protection: Wear safety goggles when handling molten wax.
Skin protection: Wear protective clothing.
71. First-aid measures
After inhalation: Remove individual to a well-ventilated area for fresh air,
and call a physician if symptoms persist.
After skin contact: Run exposed area under water for 15 minutes, then
contact a physician. Do not attempt to remove material bonded to skin.
After eye contact: Flush eyes with copious amounts of water for 15
minutes, administer first aid, and call a physician.
After swallowing: Material is not generally toxic by ingestion.
72. DENTAL INVESTMENTS
Definitions
Investing : process of covering or enveloping, wholly or in part, an
object such as a denture, tooth, wax form, crown, etc., with a suitable
investment material before processing, soldering, or casting
Investment : An investment can be described as a ceramic material that
that is suitable for forming a mold into which a metal or alloy is cast
GPT 9th ed. 2017
73. Introduction
Investment material is poured around the wax pattern whilst still in a
fluid state.
When the investment sets hard, the wax and sprue former are
removed by softening or burning out to leave a mould.
Needs to be constructed from a material which retains its integrity at
the casting temperature
Unmodified dental plasters or stones are not suitable
McCabe- Applied dental materials
74. Gypsum, phosphate, and silicate are used for investing as they can
withstand the higher temperatures of burnout and casting
procedures.
Investment material is available as a two component system
1. Powder
2. Liquid (usually water)
75. Requirements of and investing material
1. It should be capable of reproducing the shape, size, and details
recorded in the wax pattern.
2. It should be easily manipulated and must readily wet the surface
of the wax pattern.
3. It should have adequate setting time to allow the investing
procedure
4. At the same time it should harden within a relatively short period
of time.
76. 5. It should be able to withstand the high temperatures
6. It should have chemical stability at room temperature and at high
temperatures during casting.
7. It should have suffcient compressive strength at the higher casting
temperatures so that it can withstand the stresses created by molten metal
as it enters the mold
8. It should have sufficient porosity to allow the gases to escape.
77. 8. It should have a controlled expansion during setting
9. It should be easy to recover once the casting is done.
10. Smooth surface finish of the inner surface of the mold to have proper
finish of the restoration.
78. Components
Composed of three main materials
1. Refractory material,
2. Binder material,
3. Chemical modifiers
Materials used in dentistry: S. Mahalaxmi
79. 1. Refractory material
Usually it is a form of silica such as quartz, tridymite, or cristobalite
or a combination of these
Capable of sustaining exposure to a high temperature without
significant degradation.
2. Binder material
Material capable of binding the refractory material to form a coherent
solid mass
Common binders used are a-hemihydrates, ethyl silicates, or
phosphates
80. 3. Modifiers
Added to the refractory and binder materials to enhance their
physical properties.
Includes nonoxidizing agents, retarders, accelerators, and coloring
agents.
Chemical modifiers like sodium chloride, boric acid, potassium
sulfate, graphite, magnesium oxide, etc.
81. Classification
1. Gypsum-bonded investment materials: conventional casting of
inlays, onlays, crowns, and fixed partial dentures made of gold
alloys.
2. Phosphate-bonded investment materials: designed primarily for
alloys that have to be cast at higher temperatures than gold-based
alloys
3. Ethyl silicate-bonded investment materials: used in casting of
removable partial dentures with base metal alloys
Based on the binders used.
82. Type I investments: Expansion is mainly accomplished by thermal
expansion of the investment
Type II investments: Expansion is mainly through hygroscopic
expansion of the investment
Type III investments: Used for construction of partial dentures with
gold alloys.
Based upon Method of expansion
Materials used in dentistry: S. Mahalaxmi
83. Setting expansion
It is essential to understand the concept of expansion of the
investment materials.
During casting, the molten metal is forced into the investment mold
to occupy the space occupied by wax pattern before
As the molten metal cools to room temperature, it shrinks
dimensionally.
This property of metal is called casting shrinkage or solidifi cation
shrinkage.
84. Solidification shrinkage is compensated by expansion of the
investment material.
Wax shrinkage + casting shrinkage = Setting expansion +
hygroscopic expansion + thermal expansion
85. Normal setting expansion
The linear expansion that occurs during the
normal setting of the investment material
when it is surrounded by air.
There is an initial contraction during the
setting reaction as the crystals grow they
impinge on each other resulting in a net
expansion during setting.
Philips dental materials 12th edi.
86. Hygroscopic expansion
Expansion that occurs when the investment is allowed to set in
the presence of water is called hygroscopic expansion.
It takes place by either of the following ways:
1. Placing a wet liner inside the casting ring
2. Placing the invested casting ring in a water bath
3. Adding water to the exposed areas of investment during
hardening.
87. Thermal expansion
The invested casting ring is placed in an oven to burnout the wax
pattern to create a mold space.
For gypsum-bonded investments, the temperature is gradually
elevated till 700°C for no longer than 20–30 minutes.
Some amount of expansion also occurs during this process
The refractory material in the investment undergoes many
changes leading to expansion.
88. Gypsum bonded invesment
ADA SPECIFICATION NO. 126 (OLD: 2)
In 1929, Coleman and Weinstein invented a gypsum-bonded
cristobalite investment
Used for conventional casting gold alloy inlays, onlays, crowns,
and fixed partial dentures.
When this material is heated at temperatures sufficiently high to
completely dehydrate and to ensure complete castings, it shrinks
considerably and occasionally fractures.
All the three common forms of gypsum products has different
rates of thermal expansion.
Introduction of dental materials: Rechard van Noort
89. A slight expansion takes place between
400 °C and approximately 700 °C, and a
large contraction then occurs.
Above 700 °C the decomposition takes
place and contaminates the casting.
Not to be heated above 700 °C.
Philips science of dental materials 12th edi.
90. Composition
Refractory material
Silica : If the proper forms of silica are employed in the investment, this
contraction during heating can be eliminated and changed to an
expansion.
It exists in at least four allotropic forms: quartz, tridymite, cristobalite,
and fused quartz.
Quartz or cristobalite or a blend of the two in varying proportions—
65%–75% used particularly in gypsum bonded investments
91. When quartz is heated, it inverts reversibly from a “low” room-
temperature crystal form, known as α quartz, to a “high” form, called β
quartz, at a temperature of 573 °C.
This α to β phase transformation is called an inversion, and it is
accompanied by a linear expansion of 0.45%.
In a similar manner, cristobalite undergoes an analogous transition
between 200 °C and 270 °C from “low” (α cristobalite) to “high” (β
cristobalite)
Introduction of dental materials: Rechard van Noort
92. Binder
Calcium a -hemihydrate is used as the binder
On mixing with water it forms calcium sulfate dihydrate which binds
the refractory material together.
The temperature to which it is subjected should be not more than
700°C.
93. Reasons
Gypsum is not chemically stable at temperature exceeding 650°C.
When heated to temperatures above 700°C, the calcium sulfate in the
binder decomposes into sulfur dioxide and sulfur trioxides.
Contamination causes shrinkage and contamination of the metal
surface which tend to embrittle the casting metal.
94. Modifiers
Reducing agents such as carbon or colloidal copper are used to produce
nonoxidizing atmosphere within the mold when the metal is cast.
Trace amounts of boric acid and sodium chloride are added to regulate
setting time
Coloring agents are added to distinguish between various investment
materials.
Oxalates added by deteriorating with heat forming carbon dioxide and
carbon monoxide, thus preventing sulfur contamination of alloys
95. Setting time
According to ADA specification no. 2, investments should have
setting time of not less than 5 minutes or not more than 25
minutes.
Initial setting time of the modern gypsum-bonded investment is 9–
18 minutes.
96. Expansion
The total expansion is the sum of the setting expansion +
hygroscopic expansion + thermal expansion.
Designed to compensate for the average contraction of the
metal alloy being cast.
The actual amounts of expansion involved can be balanced
differently by different manufacturers
97. Normal setting expansion
As water is mixed with investment powder, it surrounds the
calcium sulfate crystals gradually converting them into calcium a
-dihydrate.
The effectiveness of setting expansion depends on the thermal
expansion of the wax pattern
The wax pattern expands due to the effect of exothermic heat
that is released from the investment while setting
98. The amount of expansion of the wax is influenced by the
softness and the thickness of the wax.
The softer the wax and the thinner the wax pattern, the more
is the expansion since the investment can move softer and
thinner wax more easily.
Amount of heat released depends on the amount of gypsum
present.
The setting expansion allowed for type I gypsum-bonded
investment is 0.6%.
99. Hygroscopic expansion
The water has to be incorporated before setting of the
investment takes place.
The water then replaces the water of hydration, thus preventing
confinement of crystal growth.
The crystals continue to grow outward in the presence of water,
resulting in more expansion.
Hygroscopic expansion is almost five to six times that of setting
expansion.
According to ANSI/ADA specification no. 2, the minimum and
maximum setting expansion for type II investment is 1.2% and
2.2%
100. Thermal expansion
The amount of thermal expansion depends on the nature and amount of
refractory material.
Also on the type of gypsum binder, water/powder ratio, and
temperature to which the mold is heated.
101. Factors influencing the setting expansion
1. Particle size of silica :
Acts as a diluent by delaying the interlocking of crystal and thus allowing
them to grow further and expand.
2. Water/powder ratio:
The greater the water content the lesser will be the binder crystals per unit
volume which in turn decreases the expansion.
3. Silica/binder ratio:
In order to increase the expansion, silica content can be increased but at the
cost of decreasing the compressive strength of the material.
The recommended ratio 65%–75% of silica, 25%–35% calcium sulfate
hemihydrate, and 3% chemical modifiers.
102. 4. Spatulation time:
More the spatulation time, more delayed will be the interlocking of
crystals, thus increasing the expansion
5. Age of the investment:
The older the investment the lower will be the hygroscopic
expansion.
6. Confinement:
The investment expansion is confined by the investment ring and wax
pattern.
7. Flow of wax:
The greater the flow of the wax, the greater will be the expansion
103. The expansion of the investment away from the wax pattern can be
enhanced by the following:
a. Placing a wet liner on the inner surface of the casting ring
b. Placing the pattern toward the outer end of the ring
c. Type of casting ring—rubber casting ring
d. Type of technique—ringless technique
104. Thermal stability
The gypsum-bonded investment decomposes above 700°C as a result
of the reaction of calcium sulfate with silica.
CaSO4 + SiO2 → CaSiO3 + SO3
The sulfur trioxide causes porosity and weakening of the investment
material.
So the gypsum bonded investments should be restricted to gold
alloys and lower melting base metal alloys which are cast below
700°C.
105. The carbon present in the residue, left after burnout procedure, reacts
with calcium sulphate to form calcium oxide and sulfur dioxide.
This reaction occurs above 700°C
This causes shrinkage and contamination of the casting with the
sulfides of the non-noble alloys.
Breakdown of gypsum above 700°C
CaSO4 + 4C → CaS + 4CO
3CaSO4 + CaS → 4CaO + 4SO2
106. Factors influencing thermal expansion
1. Type of refractory material:
Cristobalite exhibits the maximum expansion of all polymorphs of
silica.
Quartz exhibits 1.4% expansion at 600°C, while cristobalite
1.6% at 250°C, and tridymite exhibits less than 1% at 600°C.
2. Temperature:
Higher the temperature, higher will be the expansion.
Rapid heating, prolonged heating, and overheating during wax
burnout may fracture the investment and cause alloy liquid to enter
into the cracks and solidify
107. 3. Percentage and uniformity of silica:
The less uniform particle size results in greater expansion, as the
packing ability of silica is better expansion will be less.
4. Water/powder ratio:
The greater the ratio, lesser the silica content, leading to decrease in
expansion.
5. Thickness of the mold wall:
The thicker the walls of the mold, the more will be the expansion.
108. 6. Confinement:
The casting ring is the outer confinement for the investment.
The coefficient of thermal expansion of metal casting ring should
coincide with the investment material for effective expansion to
occur.
The permissible minimum and maximum thermal expansion is 0–
0.5% at 500°C and 1%–1.6% at 700°C temperatures,
109. PHOPHATE BONDED INVESTMENTS
ADA SPECIFICATION NO. 126 (OLD: 42)
Most commonly used investment in casting of palladium-
based alloys and base metal alloys
Metals which have high melting point are mainly cast by this
investment material since it is more stable at high
temperatures.
This makes it most commonly used investment materials
110. Reasons include:
Tremendous increase in the use of metalceramic and all ceramic
restorations which require higher melting alloys.
Use of more economical base metal alloys
Commercially pure titanium and titanium alloys which require
specially formulated investments to minimize the interaction of the
molten metal with the investment.
Most base metals, palladium-based metal alloys, and titanium-
based alloys are cast at temperatures of 850°C–1504°C
111. According to ANSI/ADA specification no. 42 phosphate-
bonded investments are classified into two types based on
its application:
• Type 1: For inlays, crowns, and other fixed
restorations
• Type 2: For partial dentures and other removable
restorations
112. Composition
Refractory material
Silica is the principal refractory filler in the form of cristobalite
or quartz or mixture of two components.
Used in the concentration of 80% with a particle size ranging
from submicron level to size of fi ne sand.
The filler provides refractoriness (high temperature thermal
shock resistance)and a high thermal expansion.
113. Binder
Phosphate is the binder present in this type of investment.
It present as two components
1. water soluble phosphate ion (acid)
2. the magnesium oxide
Initially phosphoric acid was used, which was later replaced
by monoammonium phosphate.
binding system undergoes an acid–base reaction between
the acidic monoammonium phosphate and the basic
magnesium oxide.
114. Modifiers
same modifiers as those of gypsum-bonded investment
Carbon can also be added to produce clean casting and
enable divesting the casting.
Carbon is not used for base metal alloys as the carbon
residues affect the final alloy composition and embrittle
the base metal alloys.
115. Liquid
liquid component consists of either water or colloidal silica
(silica sol) in water
Colloidal silica has two purposes
1. hygroscopic expansion
2. strength of the investment
For base metal alloys, 33% dilution of colloidal silica is
necessary
116. Chemistry of settting
The setting reaction is an exothermic type of reaction
Ammonium phosphate and magnesium oxide react with water to
form hydrated magnesium ammonium phosphate and water
NH4H2PO4 + MgO + 5H2O Room temperature NH4MgPO4
.6H2O + MgO + NH4H2PO4 + H2O
The set matrix consists of the multimolecular NH4MgPO. 6H2O
aggregate around excess magnesium oxide and fi llers.
117. Thermal stability
At higher temperatures, some of the remaining phosphate reacts
with silica forming complete silicophosphates
This results in a significant increase in the strength of the
materials.
Thus this investment suits almost all types of alloys, namely, base
metal alloys and palladium–silver alloys to be cast at higher
temperature.
118. Setting time
Setting time and working time for phosphatebonded
investments is relatively lesser than gypsum material.
Temperature affects setting time adversely warmer the mix, the
faster is the setting.
The longer spatulation time accelerates the reaction.
The addition of water to the silica increases the working time
119. Expansion
In the case of phosphate-bonded investments, the initial
shrinkage occurs due to decomposition of magnesium
ammonium phosphate, resulting in the liberation of ammonia
But in practice, due to the outward growth of the crystals and
inversion of silica, there is a slight net expansion.
This can be greatly increased by the use of colloidal silica partly
replacing water in the liquid.
120. The expansion of the phosphate-bonded investments mainly
depends on the thermal expansion of the material
At higher temperatures, melting alloys have higher contraction
during solidification, which necessitates a greater expansion of
the investment.
The replacement of liquid component from water to colloidal
silica increases the hygroscopic expansion.
121. The expansion of the investment differs according to the
ratio of colloidal silica to water.
As the ratio of the special liquid to water increases, the
expansion also increases.
when the ratio of colloidal silica to water is
1. When the ratio 1:3, the expansion of phosphate-bonded
investments at 700°C–900°C is 1.3%–1.5%.
2. When the ratio is 1:1, the expansion is 1.5%– 1.7%
3. When th ratio of 3:1 , th expansion is 1.7%–1.9%.
122. Phosphate-bonded investments offer greater flexibility in controlling the
amount of expansion as compared to gypsum-bonded investments.
Increased expansion results from
1. Different particle sizes of silica produce higher expansion
2. A slight modification in the liquid/powder ratio
3. The setting reaction heat softens the wax allows free setting expansion.
4. Strength of the investment material at high temperatures reduces shrinkage
of the alloy as it cools.
5. Use of colloidal silica reduces surface roughness and increases expansion
123. Ethyl Silicate bonded investment
ADA SPECIFICATION NO. 126
Also known as silicate-bonded investment or silica-bonded
investment.
Rarely used in dentistry due to the time-consuming and
complicated procedures of usage
Nowadays, mainly used for casting high-fusing base metal partial
denture alloys
This investment is available in powder and liquid form.
124. Composition
Refractory material
Powdered quartz and cristobalite act as refractory materials.
A small amount of magnesium oxide is added to the powder to reduce
the pH of silica gel during manipulation.
Binder
Silica gel in the form of sodium silicate and colloidal silica is the
commonly used binder that converts to silica at high temperatures.
125. Silica gel can be produced by
1. By adding an acid or acid salt to sodium silicate, a bonding silicic acid gel
is formed.
2. By mixing ethyl silicate with diluted hydrochloric acid to form silicic acid
solution.
Ethyl silicate is commonly used
It is the liquid component of this investment.
It is supplied as two bottles of special liquid with which the investment
powder is mixed.
126. Hydrolysis takes place between water present in the
component and ethyl silicate in the presence of hydrochloric
acid and ethyl alcohol.
The formed product is called silicic acid solution.
(C2H5O)4Si + 4H2O → Si(OH)4 + 4C2H5OH
127. Chemistry of setting
On mixing silicic acid sol with silica refractory in an alkaline
condition, a polysilicic acid or coherent gel of silica is formed.
The soft silica gel is dried at a temperature below 168°C.
During the drying, it loses alcohol and water to form a
concentrated, hard, solid, nonporous mass of cristobalite
This results in volumetric shrinkage called green shrinkage
128. Expansion
Ethyl silicate-bonded investment does not show setting expansion.
It undergoes only shrinkage during setting.
When these investments are heated to suffciently high temperatures,
considerable expansion takes place.
This investment can be heated between 1090°C and 1180°C and this
is compatible with high-fusing alloys.
The total linear expansion is equal to the total linear thermal
expansion.
Total expansion of 1.6% is attained at a temperature of about 600°C.
129. The investment procedure for ethyl silicatebonded
investment is little complicated and time consuming
Ethyl alcohol vapor liberated during hydrolysis reaction
can ignite at elevated temperatures
130.
131. Brazing investment
ADA SPECIFICATION NO. 93
The process of assembling the parts of a restoration by
soldering.
Clasps on a removable partial denture, it is necessary to
surround the parts with a suitable ceramic or investment
The parts are temporarily held together with sticky wax
until they are surrounded with the appropriate
investment material
Also called as soldering investment,
132. Composition
The investment for soldering purpose is similar to casting
investments containing quartz and a calcium sulfate
hemihydrate binder.
133. Properties
Soldering investments are designed to have lower setting
and thermal expansions than casting investments
Soldering investments do not have as fine a particle size
as the casting investment, since the smoothness of the
mass is less important
Relatively little information is available in the dental
literature on the properties of soldering investments.
134. References
1. Phillips science of dental materials, 12th ed
2. McCabe- Applied dental materials
3. Materials used in dentistry, S. Mahalaxmi.
4. Basic dental materials, Manapallil
5. Craig : Dental Materials : Properties & Manipulation
6. Introduction of dental materials: Rechard van Noort
7. S. Winkler : Essentials of Complete Denture Prosthodontics IInd Edn
8. Marzuck, operative dentistry, modern theory & practice.
9. Zhang: Rheological Characterization of Dental Waxes
10. Ito, M., Yamagishi, T. , Oshida, Y. et al. (1996) Effect of selected physical
properties of waxes on investments and casting shrinkage J Prosthet Dent.
75, 211-216
